Switch-mode power supply controller

ABSTRACT

A switch-mode power supply controller controls a circuit that includes a flyback-based, switch-mode power supply in the context of an input voltage source, a USB Type-C PD controller and an output load. The switch-mode power supply controller may be configured to estimate input voltage based on a measured magnetizing inductance discharge time. Furthermore, the switch-mode power supply controller may be configured to estimate output voltage based on the measured magnetizing inductance discharge time and the estimated input voltage. Still further, the estimated voltages may be used by the switch-mode power supply controller to limit certain currents and optimize power efficiency. Even further, the estimated and measured value may be employed by the switch-mode power supply controller to estimate and indicate brownout conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/020,496, filed Jun. 27, 2018, which is a continuation ofInternational Application No. PCT/CA2017/051207, filed Oct. 11, 2017,which claims priority to U.S. provisional Patent Application No.62/406,589, filed Oct. 11, 2016, all of which are hereby incorporatedherein by reference in their entirety.

BACKGROUND

Switch-mode power supplies (SMPSs) are important power managementcomponents in modern electronic devices. They provide, among otherthings, on-line power processing efficiency optimization, enablinglonger battery life and decreased power losses. The reduced power lossesallow for lower operating temperatures, smaller cooling solutions,reduced bill-of-material and/or decreased SMPS volume.

However, in order to implement reliable and universal on-line powerprocessing efficiency optimizations, accurate, constrained, noisetolerant and smooth controller mode transitions may be required. Thepractical implementation of such a controller is usually achieved usingexpensive, power hungry and/or application-specific mixed-signalcircuits and algorithms.

Additional difficulties with existing systems may be appreciated in viewof the instant disclosure.

BRIEF DESCRIPTION OF THE FIGURES

One or more example embodiments will now be described, by way of exampleonly, with reference to the attached figures, wherein:

FIG. 1 schematically illustrates a flyback-based, switch-mode powersupply in the context of an input voltage source, which may bealternating current (AC) or direct current (DC), a Universal Serial Bus(USB) Type-C power delivery (PD) controller, an output load and aswitch-mode power supply controller;

FIG. 2 schematically illustrates the flyback-based, switch-mode powersupply of FIG. 1 with the input voltage source, a synchronousrectification module, a multi-mode controller with on-line powerprocessing efficiency optimization and an output load;

FIG. 3 illustrates graphs of exemplary curves showing evolution of aflyback magnetizing inductance current and a differential voltage duringone switching period, where energy is transferred from a primary side toa secondary side;

FIG. 4 illustrates a graph of exemplary curves showing evolution ofoutput voltage and output load current during USB Type-C power deliveryoperation, including periods where the multi-mode controller estimatesthe input voltage and the output voltage;

FIG. 5 illustrates a state diagram representative of various modes ofoperation of the multi-mode controller of FIG. 2 during one switchingcycle;

FIG. 6 illustrates a graph of exemplary curves showing evolution of aflyback magnetizing inductance current and a flyback magnetizing voltageV_(Lm) for a medium output load with multiple valleys;

FIG. 7 illustrates graphs of graphs of exemplary curves showingevolution of an input voltage, an output voltage and a primary sidecontrol signal voltage preceding a brownout or under voltage lock out(UVLO) condition;

FIG. 8 illustrates exemplary steps in a method of detecting thebeginning of a brownout condition;

FIG. 9 illustrates exemplary steps in a method for generating atwo-dimensional lookup table of minimum flyback cell switching deviceoff-time, for on-line operation with average weighted power processingefficiency for a plurality of combinations of input voltage, outputvoltage and minimum flyback cell switching device off-time; and

FIG. 10 illustrates exemplary steps in a method of operation of themulti-mode controller from initial start-up to normal operation,including input voltage estimation, output voltage estimation, minimumflyback cell switching device off-time selection and maximum on-timeselection.

These figures depict exemplary embodiments for illustrative purposes,and variations, alternative configurations; alternative components andmodifications may be made to these exemplary figures.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Aspects of the present application relate to switch-mode power suppliesand control of universal switch-mode power supplies. Further aspectsrelate to the type of switch-mode power supplies that utilize the knownUSB Type-C power delivery (USB-PD) protocol. Still further aspectsrelate to the type of high-efficiency switch-mode power supplies thatutilize autonomous synchronous rectification.

In accordance with an aspect of the present application there isprovided a method of estimating an input voltage for a switch-mode powersupply. The method includes populating a lookup table correlating aplurality of magnetizing inductance discharge times with a plurality ofinput voltages for the switch-mode power supply, measuring a magnetizinginductance discharge time and locating, in the lookup table, an inputvoltage that is correlated to the magnetizing inductance discharge time,the correlated input voltage providing an estimate of the input voltage.

In accordance with an aspect of the present application there isprovided a method of power efficiency optimization. The method includesgenerating a plurality of theoretical power processing efficiency curvesfor a plurality of combinations of input voltage, output voltage andminimum flyback cell switching device off-time, determining an averageof a plurality of weighted power processing efficiency for the pluralityof combinations of input voltage, output voltage and minimum flybackcell switching device off-time, for each unique pair of a plurality ofunique pairs of input voltage and output voltage, selecting a particularflyback cell switching device off-time having a greatest averageweighted efficiency, populating a two-dimensional lookup table with eachparticular flyback cell switching device off-time associated with acorresponding unique pair and during on-line operation with a giveninput voltage and a given output voltage, utilizing the two-dimensionallookup table to obtain a useful flyback cell switching device off-time.

FIG. 1 schematically illustrates a circuit 100 including aflyback-based, switch-mode power supply 104 in the context of an inputvoltage source 102, which may be AC or DC, a USB Type-C PD controller108, an output load 110 and a switch-mode power supply controller 106.The circuit 100 of FIG. 1 has a primary side 100P and a secondary side100S.

The switch-mode power supply controller 106 may be implemented withmulti-mode operation capabilities for achieving on-line efficiencyoptimization over a wide range of input voltages, output voltages andoutput load currents. The switch-mode power supply controller 106 may,for example, be suited for USB-PD compliant flyback-based, switch-modepower supplies that may or may not utilize autonomous secondary-sidesynchronous rectification.

FIG. 2 illustrates components of the flyback-based, switch-mode powersupply 104 including a synchronous rectification module 203. Thesynchronous rectification module 203 may be controlled by theswitch-mode power supply controller 106. In particular, the synchronousrectification module 203 may be controlled by an on-line, powerprocessing, efficiency-optimization multi-mode controller 204. Theflyback-based, switch-mode power supply 104 includes k flyback cells: afirst flyback cell 201 a; a second flyback cell 201 b; and a k^(th)flyback cell 201 k. The k flyback cells may be referenced, individuallyor collectively, by the reference numeral 201. The flyback-based,switch-mode power supply 104 also includes k input capacitors: a firstinput capacitor 212 a across the input of the first flyback cell 201 a;a second input capacitor 212 b across the input of the second flybackcell 201 b; and a k^(th) input capacitor 212 k across the input of thek^(th) flyback cell 201 k.

Although not illustrated, a person of ordinary skill in the art ofswitch-mode power supplies will easily understand that each flyback cell201 includes a switching device and a primary side winding for a flybacktransformer 202. A distinct primary side winding is illustrated asassociated with each flyback cell 201, but not labeled separately. Themulti-mode controller 204 produces k control signals: c₁; c₂; . . . andc_(k). Each one of the k control signals is associated with acorresponding flyback cell switching device.

The flyback transformer 202 has a secondary side winding that isarranged in series with the synchronous rectification module 203. Theseries combination of the secondary side winding of the flybacktransformer 202 and the synchronous rectification module 203 providesthe output of the flyback-based, switch-mode power supply 104 across anoutput capacitor 214. A plurality, n, of reference voltages V_(ref)output from the USB Type-C PD controller 108 are received at a feedbackcompensator network 210 along with the output V_(out) of theflyback-based, switch-mode power supply 104.

The feedback compensator network 210 generates an internal error signalthat is representative of a difference between the output voltageV_(out) of the flyback-based, switch-mode power supply 104 and onereference voltage among the plurality of reference voltages output fromthe USB Type-C PD controller 108. The feedback compensator network 210processes the difference through an internal proportional-integral (PI)or proportional-integral-differential (PID) compensator. The output fromthe feedback compensator network 210 is mirrored from the secondary side100S to the primary side 100P through at an isolator 208. The isolator208 provides a control signal voltage, V_(c) ^(pri), to the multi-modecontroller 204.

When a flyback cell switching device is operated (e.g., closed), theassociated primary winding may be characterized by a magnetizinginductance value L_(m).

FIG. 3 illustrates a waveform for a flyback magnetizing inductancecurrent, i_(Lm), and a waveform for a flyback magnetizing voltage,V_(Lm), during a so-called discontinuous conduction mode (DCM) ofoperation, with so-called “first valley switching.”

The multi-mode controller 204 may be implemented as a hardware efficientsystem that executes a method for estimating the input voltage, V_(in),based on knowledge of several parameters. The parameters include anoutput voltage, V_(out), a magnetizing inductance charging time, t_(on),and a measurement of a magnetizing inductance discharging time,t_(discharge). The relationship between these parameters for theflyback-based, switch-mode power supply 104, illustrated in FIG. 1 andFIG. 2, is given by the following Equations.

$\begin{matrix}{i_{peak} = {{m_{r} \cdot t_{on}} = {{- m_{f}} \cdot t_{discharge}}}} & \left( {1a} \right) \\{\frac{m_{r}}{m_{f}} \cong \frac{v_{i\; n}}{v_{out}}} & \left( {1b} \right) \\{v_{i\; n} = {{k \cdot v_{out} \cdot \frac{t_{discharge}}{t_{on}}} = {F_{1}\left( t_{discharge} \right)}}} & (2)\end{matrix}$

In Equations (1a), (1b) and (2), the value m_(r) is representative of aslope of the waveform for the magnetizing inductance current, i_(Lm),expressed in Amperes (A) per second (s), i.e., “A/s,” in the timeperiod, t_(on), during which the magnetizing inductance current isrising (see FIG. 3). The value m_(f) is representative of a slope of thewaveform for the magnetizing inductance current, i_(Lm), expressed inA/s, in the time period, t_(discharge), during which the magnetizinginductance current is falling (see FIG. 3). Equation (2) isrepresentative of a manner of estimating the input voltage, V_(in).Estimating the input voltage through the use of Equation (2) may beshown to be both hardware efficient and accurate. The input voltageestimation represented by Equation (2) may involve use of aone-dimensional (“1-D”) lookup table in conjunction with measurement ofthe magnetizing inductance discharge time, t_(discharge).

For USB-PD compliance, the output voltage is to be regulated at 5V for acertain period of time shortly after start-up and during periods when noload is connected. Output voltage regulation is illustrated, in graphform, in FIG. 4. In FIG. 4, an output voltage waveform and an outputload current waveform are illustrated for a generic, USB Type-C PDcompliant switch-mode power supply during start-up and before, duringand after an output voltage reference change. A point 402 when the inputvoltage, V_(in), is estimated and two points 404, 406 when the outputvoltage, V_(out), is estimated are highlighted with dashed boxes. Duringlight-load modes of operation, the multi-mode controller 204 may operatewith fixed flyback cell switching device on-time, t_(on) ^(min). Thatis, the multi-mode controller 204 may use the appropriate controlsignal, c, to turn on a switching device in one of the flyback cells 201for a fixed period of time, t_(on) ^(min).

FIG. 5 illustrates a state diagram representative of various modes ofoperation of the multi-mode controller 204. The various modes ofoperation include: a first mode of operation (mode 502) for supportingDCM; a second mode of operation (mode 508) for valley switching; and askip-pulse mode of operation (mode 516).

As illustrated in FIG. 5, at start-up, the multi-mode controller 204 maybe in the first mode of operation (mode 502). Subsequent to incrementinga count (cnt), a processor (not shown) of the multi-mode controller 204may determine (step 504) whether the count is less than t_(on). Upondetermining that the count is less than t_(on), the multi-modecontroller 204 remains in the first mode of operation (mode 502). Upondetermining that the count is greater than or equal to t_(on), theprocessor of the multi-mode controller 204 re-initializes (step 506) thecount to zero and the multi-mode controller 204 enters the second modeof operation (mode 508).

Subsequent to incrementing the count, the processor of the multi-modecontroller 204 may determine (step 510) whether the count is less thant_(off) ^(min). Upon determining (step 510) that the count is less thant_(off) ^(min), the multi-mode controller 204 remains in the second modeof operation (mode 508). Upon determining (step 510) that the count isgreater than or equal to t_(off) ^(min), the processor of the multi-modecontroller 204 determines (step 512) whether a valley point has beenreached in the flyback magnetizing voltage V_(Lm). Upon determining(step 512) that a valley point has not been reached, the multi-modecontroller 204 remains in the second mode of operation (mode 508).

Upon determining (step 512) whether a valley point has been reached, themulti-mode controller 204 re-initializes (step 514) the count to zeroand determines (step 518) whether t_(on) is less than t_(on) ^(min).Upon determining (step 518) that t_(on) is less than t_(on) ^(min), themulti-mode controller 204 enters the third mode of operation (mode 516).Upon determining (step 518) that t_(on) is greater than or equal tot_(on) ^(min), the multi-mode controller 204 re-enters the first mode ofoperation (mode 502).

Often, V_(out) and t_(on) are known and the discharge time,t_(discharge), may be determined. In particular, the discharge time,t_(discharge), may be determined by measurement using a zero-voltagedetector 206 illustrated in FIG. 2. The minimum t_(on) can bepredetermined, based on multiple constraints, including: a resolution oft_(on) that minimizes limit-cycle oscillations, which are worst atsmallest t_(on); a minimized synchronous controller off-time, which isrelative to minimum t_(on); and a power processing efficiency atultra-light load.

The determination represented by Equation (2) may involve: tracking theparameter t_(on) by measuring time between start-up and a first instanceof light-load operation after start-up, e.g., detecting a fixed minimumt_(on); measuring t_(discharge) by measuring time between the firstinstance of light-load operation and a point at which the flybackmagnetizing inductance current, i_(Lm), falls to zero. The latter pointmay be detected using the zero-voltage detector 206 or a similar device;and determining the input voltage using Equation (2) coupled with theknowledge that the output voltage shortly after start-up is regulatedtightly around 5V, as specified by USB-PD, and the knowledge that thenumber of the flyback cells 201 is fixed. The determining step of thismethod may be implemented using a hardware efficient one-dimensionallookup table, which may be represented by a function, “F₁.”

FIG. 6 illustrates a waveform for the flyback magnetizing inductancecurrent, i_(Lm), and a waveform for the flyback magnetizing voltage,V_(Lm), during the second mode of operation (mode 508). The first valleypoint (mode 512), designated as 1^(st), occurs before the multi-modecontroller 204 determines (step 510) whether the count is greater thanor equal to t_(off) ^(min). Recall that the processor of the multi-modecontroller 204 determines (step 512, FIG. 5) whether a valley point(1^(st)) has been reached in the flyback magnetizing voltage V_(Lm). Assuch, the multi-mode controller 204 remains in the second mode ofoperation (mode 508) until the multi-mode controller 204 determines(step 512, FIG. 5) whether another valley point (2^(nd)) has beenreached in the flyback magnetizing voltage V_(Lm).

FIG. 7 illustrates a plot of input voltage, V_(in), a plot of controlsignal voltage, V_(c) ^(pri), and a plot of output voltage, V_(out),preceding and following a brownout condition, which may also be calledan under-voltage lock-out (UVLO) condition. Upon review of FIG. 7, itmay be seen that a decrease in the input voltage, V_(in), is associatedwith an increase in control signal voltage, V_(c) ^(pri). In aspects ofthe present application, the previously discussed estimation of theinput voltage based on Equation (2) may be expanded to cover detectinginput voltage brownout conditions. In the example plot of input voltage,the example plot of output voltage and the example plot of controlsignal voltage before and during the brownout/UVLO, each of which areshown in FIG. 7, it may be noted that, prior to brownout/UVLO, thecontrol signal voltage, V_(c) ^(pri), is increasing and that the outputvoltage is relatively constant. One consequence of a relatively constantoutput voltage is a relatively constant magnetizing inductance dischargetime, t_(discharge).

Eventually, the control signal voltage, V_(c) ^(pri), ceases to increaseand drops down to zero the beginning of a brownout condition.Experimentally, it may be found at what value of the input voltage thisdrop occurs.

With the plots of FIG. 7 in mind, it is proposed herein to consider amethod of detecting the beginning of a brownout condition. The methodmay be carried out by the multi-mode controller 204 and may involvedetermining that the input voltage is decreasing while the controlsignal voltage is increasing. Alternatively, the method may involve themulti-mode controller 204 determining that the input voltage isdecreasing despite the magnetizing inductance discharge time,t_(discharge), remaining nearly constant.

Determining that the input voltage is decreasing may, for example,involve repetitively obtaining estimations of the input voltage using anestimated or measured output voltage value, V_(out), the number, e.g.,k, of the flyback cells 201 and the ratio between t_(discharge) andt_(on) through the use of Equation (2), which is restated as follows:

$\begin{matrix}{v_{i\; n} = {{k \cdot v_{out} \cdot \frac{t_{discharge}}{t_{on}}} = {F_{1}\left( t_{discharge} \right)}}} & (2)\end{matrix}$

A hardware efficient method of estimating the output voltage, V_(out),employs an estimate of the input voltage estimate, V_(in), determinedusing Equation (2), the number, e.g., k, of the flyback cells 201, thefixed magnetizing inductance charging time, t_(on), and the measureddischarging time, t_(discharge).

Estimating the input voltage may involve use of information about theoutput load current being low, as shown in FIG. 4, during output voltagechanges, when the mode of operation is the skip-pulse mode of operation,see mode 516 in FIG. 5.

As such, a discrete output voltage estimate found using Equation (3),which follows, may be implemented using a hardware efficienttwo-dimensional (“2-D”) lookup table, which may be represented by afunction, “F₄.” Equation (3) may be shown to be hardware efficient andaccurate for output voltage, V_(out), estimation. Equation (3) mayinvolve use of one 2-D lookup table, measurement of the magnetizinginductance discharge time, t_(discharge), and estimation of the inputvoltage, V_(in).

$\begin{matrix}{v_{out} = {{\frac{v_{i\; n}}{k} \cdot \frac{t_{on}}{t_{discharge}}} = {F_{4}\left( {v_{i\; n},t_{discharge}} \right)}}} & (3)\end{matrix}$

A method of detecting the beginning of a brownout condition may employan estimate of the output voltage, V_(out), obtained, say, via Equation(3), a detected magnetizing inductance discharge time, t_(discharge),and a measurement of the flyback cell switching device on-time, t_(on).

Example steps in a method of detecting the beginning of a brownoutcondition are illustrated in FIG. 8. Upon determining (step 802) thatthe flyback-based, switch-mode power supply 104 is operating in a periodwherein the input voltage, V_(in), is decreasing and the control signalvoltage, V_(c) ^(pri), is increasing while the discharge time,t_(discharge), is relatively constant, the multi-mode controller 204 mayestimate (step 804) the input voltage, V_(in), using the parameters ofEquation (2). After each iteration of estimating (step 804) the inputvoltage, the multi-mode controller 204 may determine (step 806) whetherthe estimated input voltage is greater than a predefined voltage valuethat has been determined, say, experimentally, to be representative ofan input voltage at which a brownout condition begins. Responsive todetermining (step 806) that the estimated input voltage is less than thepredefined voltage value, the multi-mode controller 204 may drive (step808) an UVLO/brownout signal high. Responsive to determining (step 806)that the estimated input voltage is not less than the predefined voltagevalue, the multi-mode controller 204 may again estimate (step 804) theinput voltage.

Since the output voltage estimation occurs during low-load operation, aneffect of input voltage variations due to AC 100-120 Hz ripple isminimized. Notably, the accuracy of the output voltage estimate may belimited by the regulation accuracy of the feedback compensator network210.

To maximize the average power processing efficiency, it may be seen asuseful to select a minimum flyback cell switching device off-time,t_(off) ^(min). FIG. 9 illustrates example steps in a method of off-linegenerating and on-line employing of a lookup table correlating minimumflyback cell switching device off-time with pairs of input voltage andoutput voltage.

As an initial step (step 902), a processor executing a specific computerprogram generates a plurality of theoretical power processing efficiencycurves. The plurality of curves includes individual curves, where eachindividual curve may be represented by a function “η” and be generatedfor one combination among a plurality of combinations. Each combinationincludes an input voltage, an output voltage and a minimum flyback cellswitching device off-time, t_(off) ^(min). As should be clear to aperson of skill in the art of switch-mode power supplies, the flybackcell switching device off-time is typically constrained. Minimum flybackcell switching device off-time may, for instance, be constrained bymaximum switching losses. Maximum flyback cell switching device off-timemay, for instance, be constrained by peak magnetizing inductancecurrent, i_(peak) (see FIG. 3). The generation of the theoretical powerprocessing efficiency curves may be based, in part, on an assumptionthat the operation of the multi-mode controller 204 occurs in a mannerconsistent with the state diagram illustrated in FIG. 5.

The same processor may then determine (step 904) average weighted powerprocessing efficiency, η^(avg), for each combination of the plurality ofcombinations. For example, the processor may determine a powerprocessing efficiency value at a 20% load level, a 50% load level and a100% load level. These three power processing efficiency values may thenbe weighted. To find the average, the three weighted values may besummed and then divided by three.

The processor may then consider, for a unique pair of V_(in) andV_(out), which minimum flyback cell switching device off-time, t_(off)^(min), is associated with the highest average weighted efficiency,η^(avg). The processor may then select (step 906) the minimum off-time,t_(off) ^(min), that is associated with the highest average weightedefficiency. The processor may then insert (step 908) the selected forthe unique pair into a lookup table, associated with the V_(in) and theV_(out) of the unique pair. The lookup table may be represented as afunction, “F₂,” as illustrated in Equation (4), which follows:t _(off) ^(min) =F ₂(V _(out) ,V _(in)).  (4)

When useful in operation of the multi-mode controller 204, the processorof the multi-mode controller 204 may determine t_(off) ^(min) throughreading the t_(off) ^(min) associated with a given V_(in) and V_(out)combination.

A maximum flyback cell switching device on-time, t_(off) ^(max), may bedetermined such that a peak magnetizing inductance current, i_(peak)^(max), remains below a saturation current of the flyback transformer202. The maximum flyback cell switching device on-time may be based onan estimated input voltage, V_(in), according to Equation (5), whichfollows:

$\begin{matrix}{t_{on}^{{ma}\; x} = {{i_{peak}^{{ma}\; x} \cdot \frac{L_{m}}{v_{i\; n}}} = {{F_{3}\left( v_{i\; n} \right)}.}}} & (5)\end{matrix}$

Equation (5) may be simplified through the use of a lookup tablerepresented by a function, “F₃.”

FIG. 10 illustrates a top-level flowchart, illustrating example steps ina method of estimating the input voltage, V_(in), the output voltage,V_(out), the maximum on-time, t_(off) ^(max) and the minimum off-timet_(off) ^(min).

Initially, an assumption is made that V_(out) is 5V and that V_(in) ismaximized. Initial values for the maximum on-time, t_(on) ^(max), andthe minimum off-time, t_(off) ^(min) may be pre-selected based on thatassumption.

The processor of the multi-mode controller 204 determines (step 1002)whether the output voltage, V_(out), is less than a reference voltage,V_(ref). Upon determining (step 1002) that the output voltage, V_(out),is not greater than a reference voltage, V_(ref), the processorincrements (step 1012) the flyback cell switching device on-time,t_(on). The processor repeats the determining (step 1002) and theincrementing (step 1012) until the processor determines (step 1002) thatthe output voltage, V_(out), is greater than the reference voltage,V_(ref), the processor estimates (step 1004) V_(in), t_(off) ^(max) andt_(off) ^(min). In some embodiments, responsive to determining that themaximum on-time t_(on) ^(max) is greater than or equal to the flybackcell switching device on-time t_(on), the flyback cell switching deviceon-time t_(on) is assigned to the maximum on-time t_(off) ^(max).

The processor may use (step 1004) Equation (2) to estimate V_(in) basedon t_(discharge).

The processor may use (step 1004) Equation (4), with V_(out) set to 5V,to estimate t_(off) ^(min) based on the estimated V_(in).

The processor may use (step 1004) Equation (5) to estimate t_(off)^(max) based on the estimated V_(in).

The processor may then implement (step 1006) a switching cycle.

The processor may then determine (step 1008) whether the skip-pulse modeof operation (mode 516) is enabled. Determining (step 1008) whether theskip-pulse mode of operation (mode 516) is enabled may, for example,involve determining that the flyback cell switching device on-time,t_(on), has reached a flyback cell switching device on-time, t_(on)^(skip), that is already associated with the skip-pulse mode ofoperation (mode 516).

Upon determining that the skip-pulse mode of operation (mode 516) isenabled, the processor estimates (step 1010), say, through the use ofEquation (3), a new output voltage and uses the new output voltage, say,through the use of Equation (4), to find a new t_(off) ^(min). Theprocessor then returns to implement (step 1006) another switching cycle.Similarly, upon determining that the skip-pulse mode of operation (mode516) is not enabled, the processor returns to implement (step 1006)another switching cycle.

In a first aspect, there is provided hardware efficient and accurateinput voltage estimation method, requiring only one 1-D lookup table andmeasurement of the magnetizing inductance discharge time. See Equation(2).

In a second aspect, there is provided hardware efficient and accurateoutput voltage estimation method, requiring only one 2-D lookup table,measurement of the magnetizing inductance discharge time and estimationof the input voltage (via the first aspect). See Equation (3).

In a further aspect, there is provided a method for on-linecurrent-limit implementation via enforcement of a maximum on-timecompromising of 1) input voltage estimation (via the first aspect), 2)lookup of an input voltage dependent maximum on-time from a 1-D lookuptable (see Equation (5) and 3) comparison and, when applicable,limitation of issued primary-side switch on-time below the lookup tableread maximum on-time value.

In a further aspect, there is provided a method for on-line powerefficiency optimization via selection of the minimum primary sideoff-time/secondary side on-time comprising: 1) generation of powerprocessing efficiency curves for all combinations of input voltage,output voltage and minimum primary side off-time/secondary side on-timefor controller operation described in FIG. 3 using a computer programand model of switch-mode power supply. 2) Calculating average weightedefficiency (@ 20%, 50%, 100% maximum output load power) of allcombinations. 3) Selecting an off-time with a highest average weightedefficiency. 4) Populating a 2D lookup table with the off-time for thespecific input voltage and output voltage combination. 5) During on-lineoperation, utilizing an appropriate lookup table off-time entry, inaccordance with input voltage and output voltage combination andflowchart of FIG. 5.

In a further aspect, there is provided a method for robust brownout/UVLOestimation via output voltage estimation (via the second aspect),magnetizing inductance discharge time measurement and primary-sideswitch on-time knowledge. The method comprises of 1) detecting periodwhen the input voltage is decreasing, that is time when the primary-sideswitch on-time is increasing/saturated and the discharge time isrelatively constant, 2) estimating the input voltage usingmeasured/estimated parameters listed previously and the first aspect,and 3) driving an UVLO/brownout signal high when the input voltageestimate is lower than a predefined voltage value.

The example embodiments, due to use of lookup tables, may be understoodto provide hardware efficiency. The hardware efficiency can beconsidered with respect to at least some or all of: 1) the fact that 1Dand 2D lookup tables can be compactly implemented on an ASIC or an FPGA(silicon area and/or lookup table memory space are negligible); 2)lookup tables are inherently low-power, in that lookup tables eliminatemultiplication, addition, etc., which are known to be power-hungry, andlookup tables have low-propagation times, in that lookup tables can workwith very fast operating frequency; 3) the lookup table size isminimized by the proposed utilization of known load and output voltagevalues during startup and after voltage changes, see the first mode ofoperation 502 (FIG. 5); and/or 4) the zero-voltage detector 206 (FIG. 2)can be implemented using a simple and cost-effective mixed-signal(integrated or discrete) circuit such as a comparator, resistive-dividerand diode.

In some example embodiments, reference to a table herein can comprisesuitable logical constructs such as a map, mapping, single parameter ormultiple parameter computer variable, or any discrete value lookupmethod based on input variable(s).

In example embodiments, as appropriate, each illustrated block or modulemay represent software, hardware, or a combination of hardware andsoftware. Further, some of the blocks or modules may be combined inother example embodiments, and more or less blocks or modules may bepresent in other example embodiments. Furthermore, some of the blocks ormodules may be separated into a number of sub-blocks or sub-modules inother embodiments.

While some of the present embodiments are described in terms of methods,a person of ordinary skill in the art will understand that presentembodiments are also directed to various apparatus such as a serverapparatus including components for performing at least some of theaspects and features of the described methods, be it by way of hardwarecomponents, software or any combination of the two, or in any othermanner. Moreover, an article of manufacture for use with the apparatus,such as a pre-recorded storage device or other similar non-transitorycomputer readable medium including program instructions recordedthereon, or a computer data signal carrying computer readable programinstructions may direct an apparatus to facilitate the practice of thedescribed methods. It is understood that such apparatus, articles ofmanufacture and computer data signals also come within the scope of thepresent example embodiments.

While some of the above examples have been described as occurring in aparticular order, it will be appreciated to persons skilled in the artthat some of the steps or processes may be performed in a differentorder provided that the result of the changed order of any given stepwill not prevent or impair the occurrence of subsequent steps.Furthermore, some of the steps described above may be removed orcombined in other embodiments, and some of the steps described above maybe separated into a number of sub-steps in other embodiments. Evenfurther, some or all of the steps of the conversations may be repeated,as necessary. Elements described as methods or steps similarly apply tosystems or subcomponents, and vice-versa.

In example embodiments, as applicable, the switch-mode power supplycontroller 106 can be implemented as or executed by, for example, one ormore of the following systems: a Programmable Logic Controller (PLC); anApplication-Specific Integrated Circuit (ASIC); a Field-ProgrammableGate Array (FPGA); hardware; and/or software. The switch-mode powersupply controller 106 can include a processor (not shown), whichprocessor is configured to execute instructions stored in a computerreadable medium such as a memory (not shown).

The term “computer readable medium,” as used herein, includes any mediumwhich can store instructions, program steps, or the like, for use by orexecution by a computer or other computing device. The term “computerreadable medium,” as used herein, includes, but is not limited to:magnetic media, such as a diskette; a disk drive; a magnetic drum; amagneto-optical disk; a magnetic tape; a magnetic core memory, or thelike; electronic storage, such as a random access memory (RAM) of anytype including static RAM, dynamic RAM, synchronous dynamic RAM (SDRAM),a read-only memory (ROM), a programmable-read-only memory of any typeincluding PROM, EPROM, EEPROM, FLASH, EAROM, a so-called “solid statedisk,” other electronic storage of any type including a charge-coupleddevice (CCD), or magnetic bubble memory, a portable electronicdata-carrying card of any type including COMPACT FLASH, SECURE DIGITAL(SD-CARD), MEMORY STICK, and the like; and optical media such as aCompact Disc (CD), Digital Versatile Disc (DVD) or BLU-RAY Disc.

Variations may be made to some example embodiments, which may includecombinations and sub-combinations of any of the above. The variousembodiments presented above are merely examples and are in no way meantto limit the scope of this disclosure. Variations of the exampleembodiments described herein will be apparent to persons of ordinaryskill in the art, such variations being within the intended scope of thepresent disclosure. In particular, features from one or more of theabove-described embodiments may be selected to create alternativeembodiments comprised of a sub-combination of features which may not beexplicitly described above. In addition, features from one or more ofthe above-described embodiments may be selected and combined to createalternative embodiments comprised of a combination of features which maynot be explicitly described above. Features suitable for suchcombinations and sub-combinations would be readily apparent to personsskilled in the art upon review of the present disclosure as a whole. Thesubject matter described herein intends to cover and embrace allsuitable changes in technology. Certain adaptations and modifications ofthe described embodiments can be made. Therefore, the above-discussedembodiments are considered to be illustrative and not restrictive.

What is claimed is:
 1. A method comprising: measuring a magnetizinginductance discharge time of a switch-mode power supply, the switch-modepower supply comprising a plurality of flyback cells, each flyback cellcomprising a respective flyback cell switching device; locating, in afirst lookup table using the measured magnetizing inductance dischargetime, an input voltage of the switch-mode power supply that iscorrelated to the measured magnetizing inductance discharge time, thelocated input voltage providing an estimate of an actual input voltageof the switch-mode power supply; locating, in a second lookup tableusing the located input voltage, a maximum on-time value that iscorrelated to the located input voltage; and using the located maximumon-time value as a maximum on-time for the flyback cell switchingdevices.
 2. The method of claim 1, further comprising: populating thefirst lookup table with a plurality of magnetizing inductance dischargetimes correlated with a plurality of respective input voltages for theswitch-mode power supply; and populating the second lookup table with aplurality of input voltages correlated with a plurality of maximumon-time values for the switch-mode power supply.
 3. The method of claim1, further comprising: comparing the located maximum on-time value to aflyback cell switching device on-time value; and responsive todetermining that the located maximum on-time value is greater than orequal to the flyback cell switching device on-time value, using theflyback cell switching device on-time value as the maximum on-time forthe flyback cell switching devices.
 4. The method of claim 1, furthercomprising: locating, in a third lookup table using the measuredmagnetizing inductance discharge time and the located input voltage, anoutput voltage, the located output voltage providing an estimate of anactual output voltage of the switch-mode power supply.
 5. The method ofclaim 4, further comprising: populating the third lookup table with aplurality of value pairs that each include a magnetizing inductancedischarge time and an input voltage, each value pair being correlatedwith a respective output voltage of the switch-mode power supply.
 6. Themethod of claim 1, further comprising: locating, in a third lookup tableusing the located input voltage of the switch-mode power supply and anestimate of an actual output voltage of the switch-mode power supply, aflyback cell switching device minimum off-time value.
 7. The method ofclaim 6, further comprising: populating the third lookup table with aplurality of value pairs that each include an output voltage and aninput voltage, each value pair being correlated with a respectiveflyback cell switching device minimum off-time value for the switch-modepower supply.
 8. The method of claim 1, further comprising: limiting anon-line current of the switch-mode power supply by issuing aprimary-side switch on-time having an on-time value that is below themaximum on-time for the flyback cell switching devices.
 9. The method ofclaim 1, the method further comprising: repetitively determining aflyback cell switching control signal voltage; repetitively obtainingadditional measured magnetizing inductance discharge times; repetitivelylocating, in the first lookup table using the respective additionalmeasured magnetizing inductance discharge times, additional inputvoltages, the respective additional located input voltages providingrespective additional estimates of the actual input voltage of theswitch-mode power supply; detecting a period during which the flybackcell switching control signal voltage is increasing and the measuredmagnetizing inductance discharge time is constant; responsive to thedetecting, comparing a respective additional located input voltage to athreshold voltage value, the respective additional located input voltagecorresponding to the detected period; and responsive to determining thatthe respective additional located input voltage is lower than thethreshold voltage value, driving a brownout signal high.
 10. Anapparatus for controlling a switch-mode power supply, the apparatuscomprising: a zero-voltage detector of the switch-mode power supply, theswitch-mode power supply comprising a plurality of flyback cells, eachflyback cell comprising a respective flyback cell switching device; anda processor configured to: measure, based on input received from thezero-voltage detector, a magnetizing inductance discharge time; locate,in a first lookup table using the measured magnetizing inductancedischarge time, an input voltage that is correlated to the measuredmagnetizing inductance discharge time, the located input voltageproviding an estimate of an actual input voltage of the switch-modepower supply; locate, in a second lookup table using the located inputvoltage, a maximum on-time value that is correlated to the located inputvoltage; and using the located maximum on-time value as a maximumon-time for the flyback cell switching devices.
 11. The apparatus ofclaim 10, further comprising: populating the first lookup table with aplurality of magnetizing inductance discharge times correlated with aplurality of respective input voltages for the switch-mode power supply;and populating the second lookup table with a plurality of inputvoltages correlated with a plurality of flyback cell switching devicemaximum on-time values for the switch-mode power supply.
 12. Theapparatus of claim 10, wherein the processor is further configured to:compare the located maximum on-time value to a flyback cell switchingdevice on-time value; and responsive to determining that the locatedmaximum on-time value is greater than or equal to the flyback cellswitching device on-time value, use the flyback cell switching deviceon-time value as the maximum on-time for the flyback cell switchingdevices.
 13. The apparatus of claim 10, wherein the processor is furtherconfigured to: locate, in a third lookup table using the located inputvoltage and an estimate of an output voltage of the switch-mode powersupply, a flyback cell switching device minimum off-time value.
 14. Theapparatus of claim 13, further comprising: populating the third lookuptable with a plurality of value pairs that each include an outputvoltage and an input voltage, each value pair being correlated with arespective flyback cell switching device minimum off-time value.
 15. Theapparatus of claim 10, wherein the processor is further configured to:repetitively determine a flyback cell switching control signal voltage;repetitively obtain additional measured magnetizing inductance dischargetimes; repetitively locate, in the first lookup table using therespective additional measured magnetizing inductance discharge times,additional input voltages, the respective additional located inputvoltages providing respective additional estimates of the actual inputvoltage of the switch-mode power supply; detect a period during whichthe flyback cell switching control signal voltage is increasing and themeasured magnetizing inductance discharge time is constant; responsiveto the detecting, compare a respective additional located input voltageto a threshold voltage value, the respective additional located inputvoltage corresponding to the detected period; and responsive todetermining that the additional located input voltage is lower than thethreshold voltage value, drive a brownout signal high.
 16. The apparatusof claim 10, wherein the processor is further configured to: locate in athird lookup table during on-line operation of the switch-mode powersupply a flyback cell switching device minimum off-time value using agiven input voltage and a given output voltage.
 17. The apparatus ofclaim 16, further comprising: populating the third lookup table with aplurality of value pairs that each include an input voltage and anoutput voltage, each value pair being correlated with a respectiveflyback cell switching device minimum off-time value.
 18. The apparatusof claim 17, wherein: the third lookup table during off-line operationof the switch-mode power supply; and populating the third lookup tablecomprises: generating a plurality of theoretical power processingefficiency curves for a plurality of combinations of input voltages,output voltages, and flyback cell switching device minimum off-timevalues; determining an average of a plurality of weighted powerprocessing efficiencies for the plurality of combinations of inputvoltages, output voltages, and flyback cell switching device minimumoff-time values; for each unique value pair of a plurality of uniquevalue pairs of input voltages and output voltages, selecting a flybackcell switching device minimum off-time value having a greatest averageweighted efficiency; and populating the third lookup table with eachflyback cell switching device minimum off-time value associated with acorresponding unique value pair.
 19. An apparatus for controlling aswitch-mode power supply, the apparatus comprising: a zero-voltagedetector of the switch-mode power supply, the switch-mode power supplycomprising a plurality of flyback cells, each flyback cell comprising arespective flyback cell switching device; and a processor configured to:measure, based on input received from the zero-voltage detector, amagnetizing inductance discharge time; locate, in a first lookup tableusing the measured magnetizing inductance discharge time, an inputvoltage that is correlated to the measured magnetizing inductancedischarge time, the located input voltage providing an estimate of anactual input voltage of the switch-mode power supply; and locate, in asecond lookup table, an output voltage using the measured magnetizinginductance discharge time and the located input voltage, the locatedoutput voltage providing an estimate of an actual output voltage of theswitch-mode power supply.
 20. The apparatus of claim 19, wherein:populating the first lookup table with a plurality of magnetizinginductance discharge times correlated with a plurality of respectiveinput voltages for the switch-mode power supply; and populating thesecond lookup table with a plurality of value pairs that each include amagnetizing inductance discharge time and an input voltage, each valuepair being correlated with a respective output voltage of theswitch-mode power supply.